Base bias circuit, and power amplifier using the base bias circuit

ABSTRACT

A base bias circuit ( 1 ) operates like a constant voltage source, and a base bias voltage generated thereby varies according to fluctuation of the environment temperature without being influenced by the supply voltage, to hold a collector bias voltage constant. The base bias circuit ( 1 ) has a function of controlling the base bias voltage according to a control signal coming from the outside. By using a resistor ( 6 ) and resistor ( 14 ) having suitable resistances, the bipolar transistors constituting the bias circuit ( 1 ) can be small in size to reduce the electric current consumed by the bias circuit ( 1 ) thereby to make unnecessary the RF choke inductor between a power transistor ( 13 ) and the bias circuit ( 1 ). In short, the cost is lowered by making the chip size small and by reducing the number of external parts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage application of InternationalApplication No. PCT/JP01/05269, filed Jun. 20, 2001 and claims priorityto Japanese Patent Application No. 2000-183999, filed Jun. 20, 2000.

FIELD OF THE INVENTION

This invention relates to a base bias circuit for use in a poweramplifier and the power amplifier.

BACKGROUND OF THE INVENTION

A base bias circuit operating like a constant voltage source isindispensable for a power amplifier using a common-emitter bipolartransistor. The constant voltage source is more suitable than a constantcurrent source as the bias circuit from the following reasons.

It is assumed that a RF input is applied to the common-emitter bipolartransistor given a bias to a base under the constant voltage source. Incase where input RF power is sufficiently low, the common-emitterbipolar transistor operates with a low signal. Therefore, a collectorcurrent is equal to a collector bias current flowing in a such statethat no signal is given to the amplifier.

On the contrary, as the input RF power is increased, the collectorcurrent of the common-emitter bipolar transistor is increased so as toreach several times or higher of the collector bias current. Due to theincrease of the collector current, a higher saturation output and lowerdistortion can be realized.

In the meantime, in the case where the bias is given to the base underthe constant current source, the collector current is constantly kept tohFE times of the base bias current, so that the collector current is notincreased even if the input RF power is increased.

Accordingly, when the collector bias current is set in the same mannerthat the base bias is given under the constant voltage source, a gaincompression upon a high-signal operation occurs under a lower input RFpower. This degrades saturation characteristic, reduces additional powerefficiency and deteriorates linearity.

Further, when the collector bias current is equal to the collectorcurrent under such a case that the base bias is given under the constantvoltage source and the input RF power is high, a high collector currentflows even when no RF signal is given or the input RF power is low.Therefore, consumption power is problematically increased.

From the aforementioned reasons, the base bias circuit operating likethe constant voltage source is indispensable for the power amplifierusing the common-emitter bipolar transistor. Specifically, an outputresistance in a direct current state of the base bias circuit may beequal to or lower than a base input resistance in the direct currentstate of the common-emitter bipolar transistor of the amplifier.

For the base bias circuit, the following facts will be required.

At first, the bias voltage given to the base must be strictly specifiedbecause the common-emitter bipolar transistor has an extremely highmutual conductance gm.

Therefore, it is necessary that the base bias circuit has such astructure that a generated base bias voltage is not affected byfluctuation of a power supply voltage.

Moreover, the collector current of the common-emitter bipolar transistoris exponential function of temperature. Therefore, the base bias circuitmust be constituted so that the generated base bias voltage is varied independence upon fluctuation of environment temperature to keep thecollector bias current constant.

In a CDMA system portable phone, a transmission power must becontrolled. In the base bias circuit, it is therefore required that thegenerated base bias voltage is functionally variable in accordance witha control signal from the external in order to reduce the consumptionpower of a power amplifier under a low transmission power.

FIG. 2 shows an example of a conventional base bias circuit.

A base bias circuit 52 is composed of an npn type bipolar transistors53, 54, 55 and a resistor 56. All of the bipolar transistors 54, 55, 53and 58 are manufactured by the same semiconductor process, and a ratioof emitter areas is set 1:n:1:n. A collector of the bipolar transistor58 is directly connected to an RF load in a high-frequency state whileit is directly connected to a power supply in a DC state.

Initially, consideration will be made of such a case that the RF inputpower is not given. In the circuit illustrated in FIG. 2, a portionconsisting of the bipolar transistors 54, 55 and another portionconsisting of the bipolar transistors 53, 58 are symmetricallyconstituted in the DC state except that the collector of the bipolartransistor 55 is connected to the base of the bipolar transistor 54while the collector of the bipolar transistor 58 is directly connectedto the power supply in the DC state.

Herein, if the voltage VCE between the emitter and the collector is0.3-0.5 or higher, the portion consisting of the bipolar transistors 54,55 and the portion consisting of the bipolar transistors 53, 58 areconsidered to be symmetrically and completely constituted in the DCstate because the collector current of the bipolar transistor is notalmost dependent upon VCE in general. Specifically, an emitter arearatio of the bipolar transistors 54, 55 and an emitter area ration ofthe bipolar transistors 53, 58 are 1:n, respectively.

Further, the base potential of the bipolar transistor 54 is kept equalto the base potential of the bipolar transistor 53. From theabove-mentioned facts, the base-emitter voltage VBE of the bipolartransistor 55 is substantially equal to VBE of the bipolar transistor58, and VBE of the bipolar transistor 54 is substantially equal to VBEof the bipolar transistor 53.

Therefore, the collector currents flowing along the bipolar transistors55 and 58 are equal to each other while the collector currents flowingalong the bipolar transistors 54 and 53 are also equal to each other. Inthis event, the bipolar transistor 53 placed in an output portion of thebase bias circuit 52 forms an emitter follower. Taking this intoconsideration, it is found out that the output voltage of the biascircuit 52 is kept to a value lower with VBE than the base potential ofthe bipolar transistor 53. In other words, the base bias circuitoperates like the constant voltage source.

In case where this fact is analyzed in more detail, the outputresistance of the bias circuit 52, namely, the direct current resistanceviewed the side of the bias circuit 52 from the emitter of the bipolartransistor 53 is substantially equal to a direct current base resistanceof the power transistor 58.

In this event, it is assumed that hFE of the bipolar transistor issufficiently high, and the base current of the bipolar transistor 54 andthe base current of the bipolar transistor 53 are negligibly low for thecollector current of the bipolar transistor 55.

The base potential of the bipolar transistor 54 is substantially equalto 2×VBE. In the case where a voltage given to a control terminal is setto Vref and a resistance value of the resistor 56 is set to R, thecurrent flowing along the resistor 56 is given by (Vref-2×VBE)/R. Thisbecomes the collector current of the bipolar transistor 55 in almostsuch a state.

As described above, the collector currents flowing along the bipolartransistors 55 and 58 are equal to each other. Taking this intoconsideration, the collector current of the bipolar transistor 58 isalso equal to (Vref-2×VBE)/R. Therefore, it is found out that thecollector current is not affected by the power source voltage.

Herein, VBE of the bipolar transistor is generally almost constantirrespective of the collector current. Taking this into account, it isconfirmed that the collector current of the bipolar transistor 58 iscontrolled as linear function.

In this event, the bias voltage given to the base of the bipolartransistor is directly controlled. Taking this into consideration, thecollector bias current becomes the exponential function, and therefore,slight fluctuation of the base bias voltage causes large fluctuation ofthe collector bias current.

In contrast, the collector bias current becomes the linear function ofthe control voltage in the base bias circuit 52, and therefore, thefluctuation of the collector bias current for the fluctuation of thecontrol voltage is suppressed to a sufficiently low value.

Further, when the environment temperature is varied, the characteristicof each bipolar transistor is also varied. As mentioned above, in thecircuit illustrated in FIG. 2, the portion consisting of the bipolartransistors 54, 55 and the portion consisting of the bipolar transistors53 and the power transistor 58 are symmetrically constituted. To thisend, the affect of the characteristic fluctuation of the bipolartransistor 54 and the affect of the characteristic fluctuation of thebipolar transistor 53 are canceled to each other while the affects ofthe characteristic fluctuations of the bipolar transistor 55 and thepower transistor 58 are canceled to each other. As a result, such astructure is not readily subjected to the affect of the environmenttemperature.

However, the conventional technique illustrated in FIG. 2 has severalproblems.

As a first problem, the emitter area of the bipolar transistor 55 mustbe equal to the emitter size of the power transistor 58. Even if thepower transistor, for example, has an output of about 1 W for use in theportable phone, a chip size is extremely large.

Therefore, the bias circuit comprising the bipolar transistor 58 havingthe same emitter as the power transistor 58 has the chip size largerthan the power transistor 58.

As a second problem, the collector current flowing along the bipolartransistor 55 is equal to the collector bias current flowing along thepower transistor 58. This means that the consumption current of the biassupply circuit 52 is substantially equal to the consumption current ofthe power transistor 58.

As a third problem, a choke inductor 62 is necessary between the biassupply circuit 52 and the power transistor 58 in order to prevent the RFsignal from leaking to the bias circuit.

The output portion of the bias circuit 52 is structured by the emitterfollower consisting of the bipolar transistor 53. Herein, the basepotential of the bipolar transistor 53 is constantly kept to about 2×VBEby an operation of a circuit block. Taking this into account, it isfound out that the output impedance of the emitter follower consistingof the bipolar transistor 53 is relatively low under high-frequency.

Accordingly, in order to prevent the input RF signal to the powertransistor 58 from leaking to the side of the bias circuit, the chokeinductor 62 is required. In the case where an exterior part is used asthe choke inductor 62, a mounting cost and a cost for the exterior partis additionally necessary. In case where an inductor device formed on asemiconductor substrate is used as the choke inductor 62, the chip areais increased.

As the conventional technique for solving the first problem and thesecond problem, the ratio of the emitter areas of the bipolartransistors 54, 55, 53, 58 is set to 1:n:m:m×n in the bias circuitillustrated in FIG. 2.

In this case, the emitter area ratio of the bipolar transistors 54 and55 is set to 1:n, the emitter area ratio of the bipolar transistors 53and 58 is also set to 1:n, and the circuit block consisting of thebipolar transistors 54, 55 and the circuit block consisting of thebipolar transistors 53, 58 keeps symmetrical characteristic.

Therefore, functions required for the base bias circuit can be realized.Namely, the bias voltage given to the base is not affected by thefluctuation of the power supply voltage, the base bias voltage is variedin dependence upon the fluctuation of the environment temperature so asto keep the collector bias current constant, and the generated base biasvoltage is variable in accordance with the control signal from theexternal.

Further, the collector current flowing along the bipolar transistor 55becomes low with 1/m times of the collector current flowing along thepower transistor 58, and therefore, the reduction of the consumptionpower can be realized. Moreover, the emitter area of the transistorhaving the largest emitter size becomes low with 1/m times, andtherefore, the circuit area is reduced in accordance with a method ofselecting m.

However, such a third problem that the choke inductor is necessary isnot solved. Although the circuit area becomes lowest in the case of m=n,two transistor each having the emitter area of n is required, and thereis a predetermined limit for reducing the area of the bias circuit.

Moreover, although the consumption current of the bias circuit becomeslowest in the case of n=1, the bipolar transistor having the sameemitter area as the power transistor is necessary in the bias circuit,so that the circuit area is not reduced.

Thus, the conventional circuit has the limit for reducing theconsumption current and area. Further, the choke inductor for preventingthe leak of the RF power is indispensable between the base bias circuitand the power transistor, the exterior part and the additional mountingcost is necessary, or an on-chip inductor having a large area isrequired.

It is therefore an object of this invention to provide a base biassupply circuit which has a small chip area and a low consumption currentwithout a choke inductor between a base of a power transistor and a biassupply circuit and which is for use in a bipolar transistor, and anamplifier circuit using the same.

Disclosure of this Invention

A base bias circuit according to this invention supplies a bias currentto a base of a common-emitter bipolar transistor of an npn type for apower amplifier.

The base bias circuit comprises first through third bipolar transistorsof an npn type and first and second resistors integrated on asemiconductor substrate and a base bias current control terminal.

The first resistor is inserted between the base bias current controlterminal and the first bipolar transistor.

The second resistor is inserted between a base of the second bipolartransistor and the first bipolar transistor.

A base of the second bipolar transistor is connected to a collector ofthe third bipolar transistor.

An emitter of the second bipolar transistor is connected to a base ofthe third bipolar transistor.

An emitter of the third bipolar transistor is grounded. A collector ofthe first bipolar transistor is connected to a positive power supply. Anemitter of the first bipolar transistor is directly connected to thebase of the bipolar transistor for the power amplifier.

In this event, a third resistor may be inserted between a connectionpoint of the first and second resistor and a base of the first bipolartransistor, and the emitter of the third bipolar transistor may begrounded via a fourth resistor.

Further, it may be short-circuited by the use of a metal wiring insteadof the second resistor.

In addition, the first and second bipolar transistors may be replaced byn-type MOSFETs, and a buffer circuit may be inserted between the firstresistor and the base bias current control terminal.

For example, the buffer circuit comprises a fourth bipolar transistor ofan npn type and fifth and sixth resistors. An emitter of the fourthbipolar transistor is grounded and the base thereof is connected to thebase bias current control terminal via the fifth resistor.

A collector of the fourth bipolar transistor is connected to the firstresistor and the sixth resistor, and the sixth resistor is connected toa power supply terminal.

It is assumed that a resistance of a circuit consisting the firstthrough third resistors and the second and third bipolar transistors,viewed from the base of the first bipolar transistor is defied as R, amutual conductance of the first bipolar transistor is defined as gm anda common-emitter current amplification factor is defines as h21.

Under such a circumstance, an emitter area of the first bipolartransistor and resistances of the first through third resistors areselected such that an impedance given by (1/gm+R/(h21+1)) is higher thanan impedance of the base of bipolar transistor for the power amplifierin a predetermined frequency band and is equivalent to an impedance ofthe base of the bipolar transistor for the power amplifier in a directcurrent.

The first through fourth bipolar transistors may be hetero junctionbipolar transistors formed on an chemical substrate, and the firstthrough fourth bipolar transistors may be Si homo BJTs formed on a Sisubstrate.

The first through fourth bipolar transistors may be SiGe hetero junctionbipolar transistors formed on a Si substrate.

Further, the bipolar transistor for the power amplifier is formed on thesame semiconductor substrate as the base bias circuit, and the base biascircuit and the bipolar transistor for the power amplifier are connectedby a metal wiring formed by a semiconductor production process toconstitute the power amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a power amplifier according to thisinvention;

FIG. 2 is a diagram for explaining a conventional base bias circuit;

FIG. 3 is a diagram for explaining an operation of a power amplifierillustrated in FIG. 1;

FIG. 4 is a diagram for explaining an operation of a power amplifierillustrated in FIG. 1;

FIG. 5 is the other example of a power amplifier according to thisinvention;

FIG. 6 is the other example of a power amplifier according to thisinvention;

FIG. 7 is the other example of a power amplifier according to thisinvention;

FIG. 8 is the other example of a power amplifier according to thisinvention;

FIG. 9 is the other example of a power amplifier according to thisinvention;

FIG. 10 is the other example of a power amplifier according to thisinvention;

FIG. 11 is the other example of a power amplifier according to thisinvention; and

FIG. 12 is the other example of a power amplifier according to thisinvention.

BEST MODE EMBODYING THIS INVENTION

Hereinafter, this invention will be explained with reference to thedrawings.

At first, referring to FIG. 1, FIG. 3 and FIG. 4, a base bias circuit 1is composed of npn type bipolar transistors 5, 7, 9 and resistors 4, 6,14 integrated on the same semiconductor substrate.

An emitter of the transistor 5 is directly connected to a base of thepower transistor 13 without an inductor for an RF choke and resistors. Amatching circuit consisting of the base bias circuit 1, the powertransistor 13 and a passive device are fabricated on the same galliumarsenide substrate so as to totally constitute an MMIC amplifier.

Further, each of the bipolar transistors 5, 7, 9 is GaAs/AlGaAs heterojunction bipolar transistor (HBT) produced by the same process.

An area ratio of the bipolar transistors 5, 7, 9 is set to 5:1:1:30, andan emitter dimension of the bipolar transistor 7, 9 having a smallestemitter area is set to a smallest dimension permitted in the process.The total of the emitter areas of the transistors constituting the basebias circuit 1 is smaller than that of the conventional technique.

Description will be made about an operation of an amplifier circuitillustrated in FIG. 1.

A potential of a node 8 connected to the base of the bipolar transistor7 is equal to the total of VBE of the bipolar transistor 9 and VBE ofthe bipolar transistor 7. In the amplifier device, a collector currentdensity of the bipolar transistor 9 is designed so as to be equal to acollector current density of the power transistor 13.

Therefore, VBE of the bipolar transistor 9 is equal to VBE of the powertransistor 13. Further, the collector current of the power transistor 13is higher with 30 times than the collector current of the bipolartransistor 9. Accordingly, the base current of the power transistor 13is higher with 30 times than the base current of the bipolar transistor9.

The base current of the bipolar transistor 13 is equal to the emittercurrent of the bipolar transistor 5. The base current of the bipolartransistor 9 is equal to the emitter current of the bipolar transistor7. In addition, the emitter area of the bipolar transistor 5 is fivetimes of that of the bipolar transistor 7, and therefore, the collectorcurrent density of the bipolar transistor 5 becomes six times of thecollector current density of the bipolar transistor 7.

Therefore, VBE of the bipolar transistor 5 is higher than VBE of thebipolar transistor 7. Herein, the collector current of the bipolartransistor is generally proportional to exp (q×VBE/(k×T)), and takingthis into account, it is necessary that VBE of the bipolar transistor 5is higher with k×T×ln(6)/q than VBE of the bipolar transistor 7, andhigher with about 47 mV in the room temperature.

The resistance value of the resistor 6 and the resistor 14 is selectedsuch that a voltage drop due to the resistor 6 in a standard operationstate is higher with 47 mV than the voltage drop due to the resistor 14.

Herein, explanation will be made of a current value and a circuitconstant of each portion in a typical operation state of the amplifiercircuit illustrated in FIG. 1.

The collector current when the RF input power is zero, namely, thecollector bias current is 135 mA, and the collector current of thebipolar transistor 9 is 4.5 mA. The collector current density of thebipolar transistor 9 is equal to the collector bias current density ofthe power transistor 13. Since the emitter area of the bipolartransistor 9 is set to a smallest area permitted in the process, theconsumption current of the bias circuit is minimized.

The GaAs/AlGaAs hetero junction bipolar transistor for use in thesemiconductor device illustrated in FIG. 1 has hFE of approximately 30.Accordingly, the emitter current of the bipolar transistor 7 is 0.15 mA,and the base current of the bipolar transistor 7 is 0.005 mA. Further,the emitter current of the bipolar transistor 5 is 4.5 mA, and the basecurrent of the bipolar transistor 5 is 0.15 mA.

Therefore, the base current of the bipolar transistor 7 and the basecurrent of the bipolar transistor 5 are sufficiently negligibly low forthe collector current of the bipolar transistor 9. Moreover, the currentof 4.5 mA equal to the collector current of the bipolar transistor 9flows along the resistor 4. The resistance value of the resistor 6 is 12Ω, and the voltage drop due to the resistor 6 becomes 54 mV.

By contrast, the resistance value of the resistor 14 is 47 Ω, and thevoltage drop due to the resistor 14 is 7 mV. The difference between thevoltage drop due to the resistor 6 and the voltage drop due to theresistor 14 becomes 47 mV. The resistance value of the resistor 4becomes 100 Ω.

The collector current of the bipolar transistor 9 is substantially equalto the current flowing along the resistors 4, 6. Herein, the potentialof the node 8 is equal to 2.7 V as the total of the VBE of the bipolartransistor 9 and VBE of the bipolar transistor 7, and the fluctuation ofsuch a voltage is small even if the collector current of the bipolartransistor 9 is fluctuated. Taking this into consideration, thecollector current IC 9 of the bipolar transistor 9 is represented byIC=(Vref-2.7)/(100+12) by using the voltage V given to the controlterminal 2, so that IC 9=4.5 mA is obtained in the case of Vref=3.2V.

In this event, the collector bias current density of the bipolartransistor 13 is equal to that of the bipolar transistor 9 and thecollector bias current of the power transistor 13 becomes 135 mA.Herein, it is found out that the bias circuit is not affected by thepower supply voltage in such a structure because the power supplyvoltage does not appear in the equation for giving IC 9.

Moreover, when the environment temperature is fluctuated, characteristicof each bipolar transistor is also fluctuated. In the circuit shown inFIG. 1, a portion consisting of the bipolar transistors 7, 9 and aportion consisting of the bipolar transistor 5 and the power transistor13 are substantially symmetrical in the structure. Therefore, the affectof the characteristic fluctuation of the bipolar transistor 7 and theaffect of the characteristic fluctuation of the bipolar transistor 13are cancelled while the affects of the characteristic fluctuations ofthe bipolar transistor 9 and the power transistor 5 are cancelled. As aconsequence, the structure is not readily subjected to the affect of theenvironment temperature. In the circuit shown in FIG. 1, however, thesymmetrical characteristic of the circuit is destroyed because thevoltage drops due to the resistor 6 and the resistor 14 is utilized.

Therefore, the circuit is readily subjected to the affect of theenvironment temperature compared with the conventional circuitillustrated in FIG. 2. However, the voltage drops of the resistor 6 andthe resistor 14 are 54 mV and 7 mV, respectively, and are sufficientlylow in comparison with typical values (1.2-1.4 V) of VBE of theGaAs/AlGaAs hetero junction bipolar transistor.

Therefore, deterioration of resistance for the environment temperaturefluctuation due to the insertion of the resistor 6 and the resistor 14is sufficiently low.

Herein, when the resistance of the circuit consisting of the resistors4, 6, 14 viewed from the base of the bipolar transistor 5 is defined asR, the mutual conductance of the bipolar transistor 5 is defined as gm,and the common-emitter current amplification factor is defined as h21,the impedance of the base bias circuit 1 viewed the side of the bipolartransistor 5 from the node 12 is given by (1/gm+R/(h21+1)). gm of thebipolar transistor is given by q×IC/(k×T) using the collector currentIC. Since the collector current of the bipolar transistor 5 is 4.5 mA,1/gm is equal to 5.8 Ω.

On the other hand, h21 is substantially equal to hFE under a lowfrequency, is varied with a ratio of −6 dB /oct. under a high frequency,and an absolute value of h21 is equal to 1 when the frequency is acutoff frequency fT. When the collector current of the bipolartransistor 5 is 4.5 mA, fT is about 5 GHz. Therefore, h21 is about 2.5in 2 GHz as the band of the amplifier.

The resistance value of the circuit consisting of the bipolartransistors 7, 9 viewed from the node 8 is twice of reciprocal of gm ofthe bipolar transistor 9. Herein, gm of the bipolar transistor is givenby q×IC/(k×T) and the collector current of the bipolar transistor 9 is4.5 mA. Taking this into consideration, the resistance value of thecircuit consisting of the bipolar transistors 7, 9 viewed from the node8 is equal to 11.6 Ω.

If it is assumed that the voltage source is connected to the controlterminal 2, the resistance R of the circuit consisting of the resistors4, 6, 14 and the bipolar transistors 7, 9 viewed from the base of thebipolar transistor 5 becomes 47+1/(1/100+1/(12+11.6))=6.1 Ω.

As mentioned above, the impedance viewed the side of the bipolartransistor 5 from the node 12 is given by (5.8+66.1/(h21+1)). Sinceh21=hFE=30 is given under the direct current, the impedance becomesh21=2.5 under 7.9 Ω, 2 GHz. Therefore, the impedance is equal to 24.7 Ω.

A schematic diagram of frequency characteristic of this impedance isshown in FIG. 3.

In order to increase the impedance under the high frequency of the basebias circuit 1 viewed the side of the bipolar transistor 5 from the node12, the resistance value of the resistor 15 must be increased.

By simultaneously optimizing the resistance value of the resistor 6, thedifference between the voltage drop due to the resistor 6 and thevoltage drop due to the resistor 14 can be kept to a desired value,namely, to 47 mV in this case.

In this event, attention is paid for the impedance of the base of thepower transistor 13. Under the direct current, the impedance of the baseis represented by hFE/gm=hFE×k×T/(q×IC/)=30×0.026/0.135=5.8 Ω. Thisvalue is equivalent to a value (7.9 Ω) of the impedance under the directcurrent viewed the side of the bipolar transistor 5 from the node 12 ofthe base bias circuit 1.

Therefore, the base bias circuit 1 operates like the voltage sourceunder the direct current. In the meantime, the impedance of the base ofthe power transistor 13 under the high frequency is reduced to about ⅓of the value (5.8 Ω) under the direct current by the affect of thecapacitor.

By contrast, the value of the impedance under 2 GHz viewed the side ofthe bipolar transistor 5 from the node 12 of the base bias circuit 1 isequal to 24.7 Ω, and is equal to ten times of the impedance of the baseof the power transistor 13 or higher.

Therefore, the leak to the base bias circuit 1 of the signal power inthe 2 GHz band given to the power transistor 13 can be lowery suppressedwithout using the RF choke inductor between the power transistor 13 andthe bias circuit 1. The schematic diagram of the frequencycharacteristic of this impedance is shown in FIG. 4.

In summary, the base bias circuit 1 illustrated in FIG. 1 according tothis invention can realize the facts required for the base circuit foruse in the power amplifier using the common-emitter bipolar transistor.Namely, the base bias circuit 1 operates like the constant voltagesource, the generated base bias voltage is not subjected to the affectof the fluctuation of the power supply voltage, the generated biasvoltage is varied in dependence upon the environment temperaturefluctuation so as to keep the collector base current constant, and thebase bias voltage generated in accordance with the control signal fromthe external is variable.

Further, in the amplifier circuit using this invention, the resistor 6and the resistor 14 are added, and the difference between the voltagedrop due to the resistor 6 and the voltage drop due to the resistor 14is set to 47 mV, and thereby, the emitter area ratio of the bipolartransistors 7, 9 is set to 1:1 while the emitter area ratio of thebipolar transistor 5 and the power transistor 13 is set to 5:30, so thatthe symmetrical characteristic of the circuit is destroyed in such astructure.

As a consequence, the size of each bipolar transistor constituting thebias circuit 1 is smaller than that of the amplifier according to theconventional technique, and the current consumed by the bias circuit 1is reduced also. Moreover, by selecting the values of the resistors 6and 14 to suitable values, namely, 12 Ω and 47 Ω in the amplifierillustrated in FIG. 1, the impedance of the base bias circuit 1 underthe high frequency viewed the side of the bipolar transistor 5 from thenode 12 can be sufficiently higher than the impedance of the base of thepower transistor 13.

Therefore, the leak to the base bias circuit 1 of the high frequencysignal power given to the power transistor 13 can be lowery suppressedwithout inserting the RF choke inductor between the power transistor 13and the bias circuit 1.

Specifically, the cost reduction due to the reduction of the exteriorparts as well as the reduction of the chip size due to the reduction ofthe on-chip inductors can be achieved.

Subsequently, referring to FIG. 5, a base bias circuit 15 is composed ofan npn type GaAs/AlGAs hetero junction bipolar transistors 19, 20, 21and resistors 17, 18. Integrated on the same semiconductor substrate

An emitter of the transistor 21 is directly connected to the base of thenpn type GaAs/AlGaAs hetero junction bipolar transistor 22 without aninductor and a resistor for the RF choke.

A matching circuit 23 consisting of the base bias circuit 15, the powertransistor 22 and a passive device is manufactured on the same galliumarsenide substrate to totally constitute an MMIC amplifier.

The emitter area ratio of the bipolar transistors 19, 20, 21, 22 is setto 1:1:10:100, and the emitter dimension of the bipolar transistor 19,20 having a smallest emitter area is set to a minimum dimensionpermitted in the process.

The total of the emitter areas of the transistors constituting such abase bias circuit 15 is smaller than that in case using the conventionaltechnique.

The base bias circuit 15 illustrated in FIG. 5 can realize the factsrequired for the base circuit for use in the power amplifier using thecommon-emitter bipolar transistor. Namely, the base bias circuit 15operates like the constant voltage source, the generated base biasvoltage is not subjected to the affect of the fluctuation of the powersupply voltage, the generated bias voltage is varied in dependence uponthe environment temperature fluctuation so as to keep the collector basecurrent constant, and the base bias voltage generated in accordance withthe control signal from the external is variable.

Further, in the semiconductor device illustrated in FIG. 5, the resistor18 is added, and the voltage drop due to the resistor 18 is suitably setand thereby, the emitter area ratio of the bipolar transistors 19, 20 isset to 1:1 while the emitter area ratio of the bipolar transistor 21 andthe power transistor 22 is set to 10:100, so that the symmetricalcharacteristic of the circuit is destroyed in such a structure.

As a consequence, the size of each bipolar transistor constituting thebias circuit 15 is smaller than that of the semiconductor deviceaccording to the conventional technique, and the current consumed by thebias circuit 15 is reduced also. In the semiconductor device illustratedin FIG. 5, the resistance of the resistor 14 of the semiconductor deviceshown in FIG. 1 is equal to zero Ω in such a structure.

However, the emitter area of each bipolar transistor and the values ofthe resistors 17, 18 are suitably balanced, and as a result, theimpedance of the base bias circuit 15 under the high frequency viewedthe side of the bipolar transistor 21 from the node 24 is sufficientlyhigher than the impedance of the base of the power transistor 22, evenif the resistor 14 is omitted.

Accordingly, the leak to the base bias circuit 1 of the high frequencysignal power given to the power transistor 22 can be lowery suppressedwithout inserting the RF choke inductor between the power transistor 22and the bias circuit 15.

Specifically, the cost reduction due to the reduction of the exteriorparts and the reduction of the chip size due to the reduction of theon-chip inductors can be achieved.

Referring to FIG. 6, a base bias circuit 25 is composed of an npn typeSi homo bipolar transistor 30,31,32 and resistors 27, 28 integrated onthe same semiconductor substrate

An emitter of the transistor 32 is directly connected to the base of thenpn type Si homo power transistor 33 without an inductor and a resistorfor the RF choke.

The base bias circuit 25 and the power transistor 33 are manufactured onthe same Si substrate to constitute an MMIC externally added to amatching circuit.

A matching circuit 36 consisting of the passive devices is manufacturedon a dielectric substrate. In the semiconductor device shown in FIG. 6,the resistor 29 is added to the semiconductor device illustrated in FIG.5. Since the resistor 28 and the resistor 29 are equivalent with respectto the circuit operation, the operation of the semiconductor deviceshown in FIG. 6 is the same as that of the semiconductor device shown inFIG. 5 in principle.

In other words, the base bias circuit 25 illustrated in FIG. 6 canrealize the facts required for the base circuit for use in the poweramplifier using the common-emitter bipolar transistor. Namely, the basebias circuit 25 operates like the constant voltage source, the generatedbase bias voltage is not subjected to the affect of the fluctuation ofthe power supply voltage, the generated bias voltage is varied independence upon the environment temperature fluctuation so as to keepthe collector base current constant, and the base bias voltage generatedin accordance with the control signal from the external is variable.

Further, in the semiconductor device illustrated in FIG. 6, theresistors 28, 29 are added, and the voltage drop due to the resistors28, 29 is suitably set and thereby, the symmetrical characteristicbetween the emitter area ratio of the bipolar transistors 30, 31 and theemitter area ratio of the bipolar transistor 32 and the power transistor33 is destroyed in such a structure.

As a consequence, the size of each bipolar transistor constituting thebias circuit 25 is smaller than that of the semiconductor deviceaccording to the conventional technique, and the current consumed by thebias circuit 25 is reduced also. Further, the impedance of the base biascircuit 25 under the high frequency viewed the side of the bipolartransistor 32 from the node 34 is sufficiently higher than the impedanceof the base of the power transistor 33.

Therefore, the leak to the base bias circuit 25 of the high frequencysignal power given to the power transistor 33 can be lowery suppressedwithout inserting the RF choke inductor between the power transistor 33and the bias circuit 25.

Specifically, the cost reduction due to the reduction of the exteriorparts and the reduction of the chip size due to the reduction of theon-chip inductors can be achieved.

Referring to FIG. 7, a base bias circuit 37 is composed of an npn typeSiGe base bipolar transistor 39,40,41 and resistors 43, 44 integrated onthe same semiconductor substrate.

An emitter of the transistor 41 is directly connected to the base of thenpn type SiGe base power transistor 42 without an inductor for and aresistor for the RF choke.

The base bias circuit 37 and the power transistor 42 are manufactured onthe same Si substrate to constitute an MMIC externally added to amatching circuit. A matching circuit 46 consisting of passive devices ismanufactured on a dielectric substrate.

In the semiconductor device shown in FIG. 7, the resistor 28 of thesemiconductor device illustrated in FIG. 5 is omitted. Since theresistor 28 and the resistor 29 are equivalent with respect to thecircuit operation, the operation of the semiconductor device shown inFIG. 7 is the same as that of the semiconductor device shown in FIG. 6in principle.

In other words, the base bias circuit 37 illustrated in FIG. 7 canrealize the facts required for the base circuit for use in the poweramplifier using the common-emitter bipolar transistor. Namely, the basebias circuit 25 operates like the constant voltage source, the generatedbase bias voltage is not subjected to the affect of the fluctuation ofthe power supply voltage, the generated bias voltage is varied independence upon the environment temperature fluctuation so as to keepthe collector base current constant, and the base bias voltage generatedin accordance with the control signal from the external is variable.

Further, in the semiconductor device illustrated in FIG. 7, the resistor44 is added, and the voltage drop due to the resistor 44 is suitably setand thereby, the symmetrical characteristic between the emitter arearatio of the bipolar transistors 39, 40 and the emitter area ratio ofthe bipolar transistor 41 and the power transistor 42 is destroyed insuch a structure.

As a consequence, the size of each bipolar transistor constituting thebias circuit 37 is smaller than that of the semiconductor deviceaccording to the conventional technique, and the current consumed by thebias circuit 37 is reduced also. Further, the impedance of the base biascircuit 37 under the high frequency viewed the side of the bipolartransistor 41 from the node 45 is sufficiently higher than the impedanceof the base of the power transistor 42.

Therefore, the leak to the base bias circuit 37 of the high frequencysignal power given to the power transistor 42 can be lowery suppressedwithout inserting the RF choke inductor between the power transistor 42and the bias circuit 37.

Specifically, the cost reduction due to the reduction of the exteriorparts and the reduction of the chip size due to the reduction of theon-chip inductors can be achieved.

Referring to FIG. 8, a base bias circuit 48 is composed of n-channelMOSFETs 50, 51, an npn type Si homo bipolar transistor 63 and resistors65, 66 integrated on the same semiconductor substrate. A source of theMOSFET 51 is directly connected to the base of the npn type Si homopower transistor 64 without an inductor and a resistor for a RF choke.

The base bias circuit 48 and the power transistor 64 are manufactured onthe same Si substrate to constitute an MMIC externally added to amatching circuit. A matching circuit 68 consisting of the passivedevices is manufactured on a dielectric substrate.

In the semiconductor device shown in FIG. 8, the bipolar transistors 5,7 of the semiconductor device shown in FIG. 5 are replaced with theMOSFETs 50, 51. In the semiconductor device illustrated in FIG. 8, thecircuit portion consisting of the MOSFET 50 and the bipolar transistor63 and the circuit portion consisting of the MOSFET 51 and the bipolartransistor 64 has the symmetrical structure, and therefore, theoperation of the semiconductor device shown in FIG. 8 is the same asthat of the semiconductor device shown in FIG. 5 in principle.

In other words, the base bias circuit 48 illustrated in FIG. 8 canrealize the facts required for the base circuit for use in the poweramplifier using the common-emitter bipolar transistor. Namely, the basebias circuit 48 operates like the constant voltage source, the generatedbase bias voltage is not subjected to the affect of the fluctuation ofthe power supply voltage, the generated bias voltage is varied independence upon the environment temperature fluctuation so as to keepthe collector base current constant, and the base bias voltage generatedin accordance with the control signal from the external is variable.

Further, in the semiconductor device illustrated in FIG. 8, theresistors 65, 66 are added, and the voltage drop due to the resistors65, 66 is suitably set and thereby, the symmetrical characteristicbetween the ratio of the gate width of the MOSFET 50 and the emitterarea ratio of the bipolar transistor 63 and the ratio of the gate widthof the MOSFET 51 and the emitter area ratio of the bipolar transistor 64is destroyed in such a structure.

As a consequence, the size of each bipolar transistor constituting thebias circuit 48 is smaller than that of the semiconductor deviceaccording to the conventional technique, and the current consumed by thebias circuit 48 is reduced also. Further, the impedance of the base biascircuit 48 under the high frequency viewed the side of the MOSFET 51from the node 67 is sufficiently higher than the impedance of the baseof the power transistor 64.

Therefore, the leak to the base bias circuit 48 of the high frequencysignal power given to the power transistor 64 can be lowery suppressedwithout inserting the RF choke inductor between the power transistor 64and the bias circuit 48.

Specifically, the cost reduction due to the reduction of the exteriorparts added and the reduction of the chip size due to the reduction ofthe on-chip inductors can be achieved.

Referring to FIG. 9, in a base circuit 70, a buffer circuit 72 is newlyadded to the control terminal 2 of the base bias circuit 15 shown inFIG. 5. Basic operation, function and effect of the semiconductor deviceillustrated in FIG. 9 are the same as those of the semiconductor deviceshown in FIG. 5.

By adding the buffer circuit 72, the current flowing to the controlterminal 71 becomes low, so that the bias circuit 70 can be sufficientlydriven by the use of the control signal generated by an LSI manufacturedthrough the typical CMOS process.

Referring to FIG. 10, in a base circuit 76, a buffer circuit 77 is newlyadded to the control terminal 2 of the base bias circuit 15 shown inFIG. 5. Basic operation, function and effect of the semiconductor deviceillustrated in FIG. 10 are the same as those of the semiconductor deviceshown in FIG. 5.

The buffer circuit 77 serves as an inverting amplifier consisting of theresistors 78, 79 and the bipolar transistor 80. By adding the buffercircuit 77, the current flowing to the control terminal 71 becomes low,so that the bias circuit 76 can be sufficiently driven by the use of thecontrol signal generated by an LSI manufactured through the typical CMOSprocess.

Since the buffer circuit 77 is the inverting amplifier, the relationshipbetween the control voltage and the collector bias current of the powertransistor 80 is inverted in the base bias circuit 76 in comparison withthe base bias circuit 15 shown in FIG. 5.

Referring to FIG. 11, a base bias circuit 86, a power transistor 87, amatching circuit 88, and an MIN capacitor 91 for cutting DC areintegrated in the same GaAs substrate 85. As the transistors, npn typeGaAs/AlGaAs hetero junction bipolar transistors are totally used. Thematching circuit 88 is composed of a spiral inductor 89 and an MINcapacitor 90.

Basic operation, function and effect of the semiconductor deviceillustrated in FIG. 11 are the same as those of the semiconductor deviceshown in FIG. 5.

Referring to FIG. 12, base bias circuits 94, 95, power transistors 99,102, MIN capacitors 98, 100, 104, and a resistor 103 are integrated onthe same Si substrate 93. As the transistors, npn type Si homo junctionbipolar transistor are totally used.

The semiconductor device constitutes the MMIC using two stagesamplifiers, and the impedance viewed from the RF input terminal 97 inthe band of the amplifier is matched to 50 Ω by the operation of a feedback circuit consisting of the resistor 103 and the MIN capacitor 104.The matching between the stages is adjusted by an external circuit addedto the connection terminal 96 to the external circuit. The outputmatching is adjusted by the external circuit connected to the RF outputterminal 101. The base bias circuit 95 has the same basic structure asthe base bias circuit 94, and the respective circuit constants areoptimized in accordance with the difference of the emitter areas of thepower transistors 99 and 102. Basic operation, function and effect ofthe base bias circuits 94 and 95 are the same as those of the base biascircuit 15 shown in FIG. 5.

Industrial Applicability

According to this invention, the chip area and the consumption currentcan be reduced, and the choke inductor between the base of the powertransistor and the bias supply circuit is unnecessary.

1. A base bias circuit which supplies a bias current to a base of acommon-emitter bipolar transistor of an npn type for a power amplifier,wherein: the base bias circuit comprises first through third bipolartransistors of an npn type and first and second resistors integrated ona semiconductor substrate and a base bias current control terminal, thefirst resistor is inserted between the base bias current controlterminal and the first bipolar transistor, the second resistor isinserted between a base of the second bipolar transistor and the firstbipolar transistor, a base of the second bipolar transistor is connectedto a collector of the third bipolar transistor, an emitter of the secondbipolar transistor is connected to a base of the third bipolartransistor, an emitter of the third bipolar transistor is grounded, acollector of the first bipolar transistor is connected to a positivepower supply, and an emitter of the first bipolar transistor is directlyconnected to the base of the bipolar transistor for the power amplifier.2. A base bias circuit as claimed in claim 1, wherein: a third resistoris inserted between a connection point of the first and second resistorand a base of the first bipolar transistor.
 3. A base bias circuit asclaimed in claim 2, wherein: when a resistance of a circuit consistingthe first through third resistors and the second and third bipolartransistors, viewed from the base of the first bipolar transistor isdefied as R, a mutual conductance of the first bipolar transistor isdefined as gm and a common-emitter current amplification factor isdefines as h21, an emitter area of the first bipolar transistor andresistances of the first through third resistors are selected such thatan impedance given by (1/gm+R/(h21+1)) is higher than an impedance ofthe base of bipolar transistor for the power amplifier in apredetermined frequency band and is equivalent to an impedance of thebase of the bipolar transistor for the power amplifier in a directcurrent.
 4. A base bias circuit as claimed in claim 1, wherein: theemitter of the third bipolar transistor is grounded via a fourthresistor.
 5. A base bias circuit as claimed in claim 1, wherein: theemitter of the third bipolar transistor is grounded via the fourthresistor, and is short-circuited by the use of a metal wiring instead ofthe second resistor.
 6. A base bias circuit as claimed in claim 1,wherein: the first and second bipolar transistors are replaced by n-typeMOSFETs.
 7. A base bias circuit as claimed in claim 1, wherein: a buffercircuit is inserted between the first resistor and the base bias currentcontrol terminal.
 8. A base bias circuit as claimed in claim 7, wherein:the buffer circuit comprises a fourth bipolar transistor of an npn typeand fifth and sixth resistors, an emitter of the fourth bipolartransistor is grounded and the base thereof is connected to the basebias current control terminal via the fifth resistor, a collector of thefourth bipolar transistor is connected to the first resistor and thesixth resistor, and the sixth resistor is connected to a power supplyterminal.
 9. A base bias circuit as claimed in claim 8, wherein: theforth bipolar transistor is a hetero junction bipolar transistor formedon a chemical substrate.
 10. A base bias circuit as claimed in claim 8,wherein: the fourth bipolar transistor is a Si homo BJT formed on a Sisubstrate.
 11. A base bias circuit as claimed in claim 8, wherein: thefourth bipolar transistor is a SiGe hetero junction bipolar transistorformed on a Si substrate.
 12. A power amplifier, wherein: the bipolartransistor for the power amplifier is formed on the same semiconductorsubstrate as the base bias circuit as claimed in claim 1, and the basebias circuit and the bipolar transistor for the power amplifier areconnected by a metal wiring formed by a semiconductor productionprocess.
 13. A base bias circuit as claimed in claim 1, wherein: thefirst through third bipolar transistors are hetero junction bipolartransistors formed on a chemical substrate.
 14. A base bias circuit asclaimed in claim 1, wherein: the first through third bipolar transistorsare Si homo BJTs formed on a Si substrate.
 15. A base bias circuit asclaimed in claim 1, wherein: the first through third bipolar transistorsare SiGe hetero junction bipolar transistors formed on a Si substrate.